The present invention relates to an automotive vehicle cruise control system and, more particularly, to a method of controlling vehicle speed with improved gear shifting for an automatic transmission.
Automotive vehicles generally incorporate a motive force system having three basic components: an engine, a drivetrain and drive wheels. The engine produces force by converting chemical energy from a liquid fuel into the mechanical energy of motion. The drivetrain transmits the resultant force of this kinetic energy to the wheels which frictionally contact a surface for moving the vehicle. The main component of the drivetrain is the transmission, which transmits engine torque over a relatively limited angular speed range to the wheels over a broader speed range, in accordance with the tractive-power demand of the vehicle. The transmission also controls the direction of rotation applied to the wheels so that the vehicle may be driven both forward and backward.
One advanced type of transmission is a multiple speed electronically controlled automatic transmission with overdrive. Examples of this type of electronically controlled automatic transmission are described in U.S. Pat. No. 4,875,391, entitled xe2x80x9cAn Electronically-Controlled, Adaptive Automatic Transmission Systemxe2x80x9d, issued on Oct. 24, 1989 to Leising et al.; U.S. Pat. No. 4,905,545, entitled xe2x80x9cMethod of Controlling the Speed Change of a Kickdown Shift for an Electronic Transmission Systemxe2x80x9d, issued on Mar. 6, 1990 to Leising et al.; U.S. Pat. No. 4,951,200, entitled xe2x80x9cMethod of Controlling the Apply Element During a Kickdown Shift for an Electronic Automatic Transmission Systemxe2x80x9d, issued on Aug. 21, 1990 to Leising et al.; and U.S. Pat. No. 5,669,850, entitled xe2x80x9cShift Hunting Prevention For An Automatic Transmissionxe2x80x9d, issued to Dourra et al. These patents are owned by the Assignee of the present application and are incorporated herein by reference. However, it should be appreciated that the principles of the present invention are not limited to any particular automatic transmission, and that the present invention may be applied to a wide variety of other powertrain configurations.
A vehicle is generally equipped with an electronic engine control system for controlling the operation of the engine and drivetrain of the vehicle. The electronic control system includes a microcomputer-based transmission control module capable of receiving and monitoring input signals indicative of various vehicle operating conditions such as engine speed, torque converter turbine speed, vehicle output speed, throttle angle position, brake application, hydraulic pressures, a driver selected gear or operating condition (PRNODDL), engine coolant temperature and/or the ambient air temperature. Based on the information contained in the monitored signals, the controller generates command or control signals for causing actuation of solenoid-actuated valves to regulate the application and release of fluid pressure to and from apply cavities of clutches or frictional elements of the transmission. Accordingly, the controller is typically programmed to execute predetermined shift schedules stored in memory of the controller through appropriate command signals to the solenoid-actuated valves.
In addition to controlling the vehicle operation based on a manual operator throttle input, a large number of today""s vehicles are also equipped with a cruise control system for allowing automatic speed control of the vehicle. The conventional cruise control system generally includes an operator input for selecting a desired setpoint speed, an operator input for incrementally increasing and/or decreasing the desired setpoint speed and a resume speed control input to resume cruise control operation with a previously selected setpoint speed. As is commonly known, the basic cruise control system operates to control the engine throttle position so as to attempt to continually maintain the vehicle speed at or near the desired setpoint speed.
With vehicles equipped with an automatic transmission, the cruise control system may cause various repetitive and cyclical up-shifting and downshifting of the automatic transmission as the transmission controller follows the predetermined shift schedules that are generally programmed in memory. For example, when traveling uphill, especially uphill on a steep incline, the transmission controller may up-shift and downshift between gears several times in order to maintain the vehicle speed at or near the desired setpoint speed. Cyclical up-shifting and downshifting of the transmission to maintain a speed setpoint can lead to a xe2x80x9cshift huntingxe2x80x9d condition. Repeated up-shifts and downshifts in turn affect the overall sound and feel of the vehicle which can be noticeable to the driver and passengers. In addition, the individual up-shifts or downshifts of the conventional automatic transmission can cause a sudden momentary increase or decrease in acceleration in an abrupt manner, especially when such changes cause large engine speed changes.
In conventional cruise control systems, many factors are considered in the methodology for determining when a shift between a first and a second gear is desirable. For example, the speed of the vehicle, throttle angle and manifold air pressure are compared to a set of predetermined setpoints to determine if an up-shift is feasible. These setpoints, typically derived from testing, do not account for variations in the loads acting on the vehicle such as changes in road topography, road surface, aerodynamics, or other loads acting on the engine such as increased electrical load, change in operation of an air-conditioning compressor or change in fuel quality. These changes, while directly affecting the performance of the engine, are not inherently easy to measure and thus do not allow for relatively easy monitoring of the performance of the engine.
It is therefore desirable to monitor the output performance of the engine in a real time basis to accurately show the output of the engine for use in cruise control operation. Additionally, it is desirable to predict the maximum output of the engine for use in determining cruise control operation. Furthermore, it is desirable to combine the current real time engine output performance and predicted engine output performance to accurately determine the current loads acting on the vehicle or engine which would preclude an engine up-shift.
To achieve the foregoing objectives, the present invention provides an interactive cruise control system and automatic transmission for a vehicle with improved shifting of the automatic transmission. The automatic system and method controls gear shifts of the transmission so as to prevent the occurrence of shift hunting. With the transmission engaged in a first gear, the output torque required to maintain a predetermined speed in the first gear is determined and a maximum output torque available in an up-shift condition to a second gear is predicted. An up-shift from the first gear to the second gear is inhibited when the predicted maximum output torque available in the second gear is less than the determined output torque required to maintain the predetermined speed in the first gear. An up-shift is allowed once the determined maximum output torque available in the second gear exceeds the output determined torque required to maintain the predetermined speed in the first gear.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.